1. Field of Invention
The invention relates to a control unit of an automatic transmission and, more particularly, to a control unit integrally combining a neutral start switch mounted on an automatic transmission main body and an electronic control device for transmission control.
2. Description of Related Art
Conventional automatic transmissions use an electronic control device to control a hydraulic pressure control device incorporated in the automatic transmission main body so as to automatically perform speed-shift within a range selected by the driver. The automatic transmission main body and the electronic control device are installed in separate locations of a vehicle and undergo thorough quality control as separate components. Quality control processes are also required when these components are connected and finally installed in the vehicle to ensure that they perform as desired. Because the connection between the automatic transmission main body and the electronic control device is performed at the stage of installation in a vehicle, it is impossible to "de-bug" or adjust the control of the one-to-one correspondence between the automatic transmission main body and the electronic control device before the installation stage. Therefore, it is necessary to adjust the automatic transmission and the counterpart electronic control device so that they conform to each other after they are installed in a vehicle. Accordingly, many manhours are required to perform the difficult task of quality control for automatic transmissions.
In addition, because the two components are installed in different locations in the vehicle, a long wire harness is needed to connect the components, thereby increasing the susceptibility to electromagnetic noise and requiring a labor intensive wiring arrangement. Further, significant space for wiring is also required. Thus, for the reasons stated above, the process for ensuring total quality control for automatic transmissions faces various problems.
Attempts have been made to solve the aforementioned problems by combining an automatic transmission main body and an electronic control device into a single unit. As an example of such attempts, Japanese Patent Publication No. Hei 5-70023 discloses an apparatus in which an automatic transmission main body and an electronic control device are integrally combined by incorporating the electronic control device into a case of a neutral start switch. The neutral start switch is conventionally disposed on an automatic transmission casing for outputting an electric signal to the electronic control device indicating a range position as selected by a driver of the vehicle.
However, the neutral start switch not only provides an electric signal output to the electronic control device for indicating a driving range position, but also switches drive circuits on and off for driving the starter motor and turning on the reverse lamp and similar devices. That is, the neutral start switch inevitably performs operations for contacting and separating a stationary contact and a movable contact by mechanical switching actions. Therefore, production of metal dust by the abrasion between contacts that slide on each other is inevitable. To reduce such abrasion and operating resistance, grease is normally applied to the contacts. However, because electrical arcs are produced when mechanical contacts come into and out of contact with each other, grease or metal dust or a mixture thereof is often scattered by the arcs. The scattered metal dust and grease deposit and accumulate on the circuit base board of the electronic control device and, therefore, smear and damage the base board such that circuit operation is adversely affected. Presently, the industry lacks a device that addresses this problem and, therefore, no particular measure for solving the problem is known in the art.